The invention concerns a shoe sole with an upper sole part consisting of wood, whose upper side, which is preferably orthopedically shaped, forms the support for the sole of the foot, and a running sole made of elastic and flexible material which is arranged beneath the upper sole part, whereby the upper sole part is divided, at least in the ball region, into several strips running crosswise to the lengthwise direction of the sole, and these strips are joined together by flexible intermediate pieces, preferably made of polyurethane foamed onto the wood. Further, the invention concerns a process for the manufacture of such a shoe sole.
Shoe soles with an upper sole part consisting of wood and with a running sole made of elastic and flexible material which is attached to the under side of this upper sole part have been known for a long time. Such shoe soles have the advantage that they have excellent support hygienic properties, since they absorb perspiration and control moisture, and that they support the foot in an orthopedically correct manner, particularly if the upper side of the upper sole part is shaped orthopedically. However, there is the disadvantage in shoe soles, whose upper sole part consists wholly of wood, that its rigidity does not make possible in such shoe soles a bending in the ball region, as is necessary for comfortable walking.
In order to eliminate this disadvantage, it has already been proposed to divide the upper sole part consisting of wood in the ball region and to connect the individual parts by flexible intermediate pieces, particularly of polyurethane foamed onto the wood. The arrangement of several flexible intermediate pieces offers the advantage of a better bendability. In this case, however, the strips found between the flexible intermediate pieces in the longitudinal direction of the sole must be narrow in order to be able to arrange all of the elastic intermediate pieces in the ball region. The longitudinal direction of the fibers of the wood runs usually in the longitudinal direction of the sole in the shoe soles, and the division of the upper sole part into strips thus runs crosswise thereto. Now, if the individual strips are narrow, there is the danger that with an unequal load of the same, the strips will break along the longitudinal direction of the fibers of the wood, thus crosswise to the longitudinal direction of the strips. Such an unequal load will occur, for example, if uneven surfaces are tread upon with the sole. Thus, if one treads upon small stones with the shoe sole, this may cause the breaking of one or more strips.
Therefore, the task of the present invention is to avoid this disadvantage and to form a shoe sole in which the danger of breaking the narrow strips is avoided. A solution to this task according to the invention, proceeding from a shoe sole of the type described initially, consists of the fact that the under side of the upper sole part is joined rigidly on the surface with a reinforcing layer at least in the region of the strips. This reinforcing layer effects a reinforcement of the strips crosswise to the longitudinal direction of the fibers of the wood, as a consequence of the rigid surface combination with the under side of the upper sole part, whereby the danger of breaking is excluded even with nonuniform loading of the sole.
According to a preferred form of embodiment of the invention, the reinforcing layer consists of at least one layer of wood veneer attached, preferably glued, to the under side, of the upper sole part. Frequently a single layer consisting of a wood veneer is sufficient for reinforcement. Sometimes, however, it is appropriate to provide several layers, preferably joined together by gluing, whereby if there is produced a diagonal and crosswise gluing of neighboring layers with respect to the longitudinal directions of the fibers, a plywood is formed, which then forms the reinforcing layer. The use of such a wood veneer or such a plywood has the advantage that a solid surface connection, preferably by means of gluing, can be obtained, which is necessary for producing the aimed-at effect, as a consequence of the uniformity of the materials both for the upper sole part as well as for the reinforcing layer.
With the use of a wood veneer as a reinforcing layer, it is of advantage if the longitudinal direction of the fibers runs perpendicular to the longitudinal direction of the fibers of the upper sole part consisting of wood, at least for one of the layers of wood veneer, since then the reinforcement of the individual strips is produced particularly in any direction in which there is a danger of breaking. If a single layer is provided of a wood veneer, then the longitudinal direction of the fibers of this single layer is to be arranged perpendicular to the longitudinal direction of the fibers of the upper sole part consisting of wood. With the use of plywood, which is formed, for example, from three diagonal and cross-glued layers of a wood veneer, it is appropriate to allow the longitudinal direction of the fibers of the two outer layers to run perpendicular to the longitudinal direction of the fibers of the upper sole part consisting of wood and to allow the middle layer to run crosswise thereto.
However, the reinforcing layer may also consist of a plastic part attached by the surface to the under side of the upper sole part. In the simplest case, the reinforcing layer is formed by a plastic foil glued onto the under side of the upper sole part. However, a hardenable, but not yet hardened plastic material, for example, can be coated onto the under side of the upper sole part, for example, by means of spraying or applying with a spatula, and this forms the reinforcing layer after hardening.
The reinforcing layer may also extend over any region of the under side of the upper sole part, in which the intermediate pieces are arranged. However, it is appropriate, if the surface of the under side of the upper sole part formed by the intermediate pieces does not have the reinforcing layer. In this case, since this is particularly appropriate for a simple manufacture of the sole of the invention, the intermediate pieces and the running sole are formed in one piece, since then the reinforcing layer does not form a separation between the intermediate pieces and the running sole.
Another solution to the task of the invention, proceeding from a shoe sole of the type described initially, consists of forming the strips from at least two parts, whose neighboring front surfaces essentially run in the longitudinal direction of the sole and are also joined together by flexible intermediate pieces. In this way, a shoe sole is formed in which the strips can be bent crosswise to their longitudinal direction, thus as a rule in the longitudinal direction of the fibers of the upper sole part consisting of wood, so that in this case also, the danger of breaking these strips with an uneven load is eliminated. It is appropriate, if all of the intermediate pieces are formed in one piece and are thus joined together, so that a good cohesion is also assured between the individual intermediate pieces, and the manufacture of the shoe sole of the invention is simplified.
The process of the invention for manufacturing the described shoe sole essentially consists of the fact that after a reinforcing layer is rigidly joined on the surface, preferably by gluing or with an adhesive, to the under side of a wood piece forming the upper sole part, at least in the ball region, several cuts are produced in this under side in the ball region, for example, by milling, by means of which in the presence of a reinforcing layer, this is layer fully separated and the wood piece forming the upper sole part is at least partially separated, such that this wood piece, if necessary with the reinforcing-layer segments joined rigidly therewith, is inserted into a mold, that a liquid plastic material, preferably a material forming polyurethane, is introduced hereon in the mold, and solidifies, particularly by foaming out, whereby in the region of the cuts, the intermediate pieces and the running sole thus formed in one piece are formed, and that finally the sole part thus manufactured is removed from the mold. The wood piece forming the upper sole part thus need not have the exact [final] form of the upper sole part, but may also be larger; particularly, it may have a greater thickness measured perpendicularly to the upper side of the sole. In this case it is possible to incompletely separate the wood piece forming the upper part of the sole, while a joining is retained on the upper side, whereby the insertion into the mold is essentially simplified. According to another feature of the process of the invention, after demolding, at least the upper side of the wood piece forming the upper sole part is processed, preferably by milling or grinding, and removing excess material, whereby not only the orthopedic shaping of this upper side can be achieved, but also any region can be eroded in which there is still present a joining of the wood part forming the upper sole part, and thus the intermediate pieces reach to the upper side of the upper sole part.